A small subgroup of atopic dermatitis (AD) patients, suffer from life-threatening disseminated herpes simplex virus (HSV) skin infections, termed eczema herpeticum (ADEH+). The manifestation of ADEH+ is not simply a consequence of HSV-1 infection, as latent infection of both the AD and general population is near universal (90%). Most importantly, there is a remarkable bimodality in the `recurrence' of EH episodes; most individuals have only a single episode, but a subgroup of ADEH+ have more than five (5+) lifetime episodes. Based on this, we hypothesize recurrent ADEH+ is characterized by unique: (1) genetic profiles, (2) dysregulated skin tissue transcriptional signatures, and (3) skin cell responses to HSV-1 infection, which collectively underlie ADEH+ disease development. We suggest these profiles, signatures, and responses will be most pronounced among AD patients with 5+ EH episodes as they represent the extreme of AD severity. Therefore we propose an extreme trait study, investigating recurrent ADEH+ (5+ episodes) vs. ADEH-, using genetic, transcriptomic, and cellular function analyses. The specific aims will be: 1) To use whole genome sequencing (WGS) to identify rare deleterious genetic variants that determine recurrent ADEH+. Deep WGS data will be generated on 50 ADEH+ subjects with >5 EH episodes. We will leverage the ADRN DNA repository and expertise on WGS data from 500 ADEH- individuals through our ongoing ADRN protocol on S. aureus colonization as a control group; 2) To identify differences in the transcriptional signatures of recurrent ADEH+ vs. ADEH- in disease-relevant tissue and cells under baseline and HSV-1 stimulated conditions. We will isolate dermal and epidermal tissue from uninvolved skin biopsies of recurrent ADEH+ versus ADEH- subjects. We will also isolate plasmacytoid dendritic cells from the peripheral blood of these subjects. Paired tissues and cells from these subjects will be sham- and HSV-1-infected. Whole transcriptome RNA-sequencing (RNA-seq) will be performed on these samples. We will determine tissue/cell specific genes regulated by HSV-1 infection and whether this regulation differs by ADEH status. Differential and allele-specific expression data will be used to filter Aim 1 risk variants; 3) Compare primary cell responses to HSV-1 infection between recurrent ADEH+ vs. ADEH- and determine biological function of risk genes and genetic variants identified from WGS and RNA-seq analyses. We will culture skin primary keratinocytes and fibroblasts from the same subjects examined in Aims 1 and 2. Part 1: Paired sham and HSV-1 infected cultures will be analyzed to determine differences in the infection rates and anti-viral, inflammatory, and differentiation responses between ADEH+ and ADEH- subjects. Part 2: We will functionally characterize the effect of genes and genetic risk variants (identified in Aims 1 and 2) on these cellular HSV-1 responses by a suite of genetic modification techniques applied to these primary cells, including CRISPR/Cas9 mediated gene-editing. Our novel, integrated, multi-disciplinary extreme trait design will allow a powerful examination of the etiology of ADEH+.